1. Field of the Invention
The present invention relates to a medical device and to a method in a medical device according to the preambles of the independent claims adapted to detect and monitor Pulmonary Artery Pressure (PAP). In particular the invention relates to a medical device and to a method adapted to detect and monitor Pulmonary Artery Hypertension (PAH) or Heart Failure (HF).
2. Description of the Prior Art
Heart failure is the failure of your heart muscle to pump enough blood to meet your body's needs. About 4.8 million people in the United States have heart failure. It is the major cause of admission to the hospital for those over 65 years old. There are many reasons why the heart muscle becomes weak.
When the heart muscle pump cannot handle the amount of blood it gets, the blood slows down and backs up. This puts pressure on the blood vessels in the lungs, legs and abdomen and causes leaking from these blood vessels. Fluid collects in the tissues, which can cause you to have leg swelling, shortness of breath, lack of appetite or abdominal pain. This backup of blood is called heart failure. The heart chambers get bigger over time to decrease the backup. Although this helps in the early stages, it makes the heart pump worse in the long run. Cardiomegaly is the name for when the heart chamber gets bigger.
There are many reasons why the blood backs up. The heart may become stressed and cannot pump as well. The amount of blood (fluid) that the heart has to pump may increase. Heart failure decreases the kidney's ability to remove salt (sodium) and water from your body. Because your kidneys get less blood, they think that the body needs more blood volume. To make up for this, your body puts out a hormone that makes you hold salt and water. This hormone increases as the heart's pumping ability becomes worse. That is why fluid retention becomes worse as the heart becomes weaker.
The pressure in the pulmonary artery is usually much lower than in the aorta. As a natural way to deal with this the left ventricle is much stronger than the right ventricle and can therefore deal with the higher pressures and higher pressure gradients in the left side. However, when pressure increases on the right side, the right ventricle is not equipped to handle the increased demand on myocardial performance. Hypertrophy most likely occurs and this will inevitably lead to right-sided heart failure. Symptoms may then be swollen feet as a result of fluids backing up in the body as the right side of the heart can not manage to pump away the blood returning from the body, due to the high pressure required to open the pulmonary valve, causing the congestion. This is known as peripheral oedema.
Pulmonary artery hypertension (PAH), also referred to as pulmonary hypertension (PHT), is often idiopathic and the patients are also often symptom free for quite some time. These two facts lead to that this disease often goes on unnoticed for quite some time, delaying any potential care. Two types of PAH may be identified: Primary pulmonary arterial hypertension (PPAH) that is inherited or occurs for no known reason and Secondary pulmonary arterial hypertension (SPAN) that either is caused by, or occurs because of, another condition. The condition includes chronic heart or lung disease, blood clots in the lungs, or a disease like scleroderma.
Described more in detail, PAH is continuous high blood pressure in the pulmonary artery and the average blood pressure in a normal pulmonary artery is about 14 mmHg when the person is resting. In PAH, the average blood pressure is usually greater than 25 mmHg. The disease, which has no cure, causes continuous high blood pressure in the artery that carries blood from the heart to small vessels in the lungs. The muscles within the walls of the arteries may tighten up. This makes the inside of the arteries narrower. The walls of the pulmonary arteries may thicken as the amount of muscle increases in some arteries. Scar tissue may form in the walls of arteries, and as the walls thicken and scar, the arteries become increasingly narrow. Tiny blood clots may form within the smaller arteries, causing blockages. As the vessels narrow, less room is left for blood to flow. The heart can't keep up if the pressure gets too high, and excessively high pressure in the pulmonary artery can cause liquid to leak through the capillary walls and into the lungs. That causes symptoms including fatigue, dizziness, shortness of breath, palpitations or abnormal heartbeat, dry cough, chest pain, swollen ankles or legs, and has frequent fainting spells, eventually heart failure and death. PAH can be inherited, or result from another chronic heart or lung disease.
There are different plausible causes of PAH. It may be due to an already present left-sided heart failure causing pulmonary venous hypertension, then backing up. In such cases it is likely that a left-sided heart failure already was detected, but there are cases where the PAH occurs without any left-sided events. Examples of such reasons include chronic obstructive pulmonary disease (COPD), congenital heart disease, rheumatologic or liver diseases, HIV infection, pulmonary embolism, or any lung disease causing hypoxia (lower levels of oxygen in the blood). Sleep apnea is also a possible reason for PAH. Currently, the disease is often fatal within months of diagnosis.
There are no distinct, common causes to this disease and it is usually not discovered until the right side of the heart has started to fail. This is yet another aspect of why it is considered to be very important to discover the onset of PAH at an early stage.
The treatments for severe PAH include initially medications and additional oxygen, but later on—lung transplant. Transplanting the lung is the most dangerous and least successful of all organ transplants that are performed today. Complications are both common and severe and most patients only live a couple of years.
United States Patent Application Publication No. 2006/0116590 relates to endocardial pressure differential sensing systems and methods for determining a pressure differential between a left heart chamber and a right heart chamber that may be used for detecting different cardiovascular conditions and discriminating between the conditions. The pressure detection is performed by an implantable medical device having leads in different heart chambers and where pressure sensors are provided on the leads. An example of a detectable condition is pulmonary artery hypertension (PAH). PAH is characterized by a rapid increase in the pressure differential, when the sensed pressure in the left chamber remains relatively constant.
United States Patent Application Publication No. 2006/0167359 relates to an implantable medical device with a sensor for sensing hemodynamic pressure over time. The pressure data is processed to form hemodynamic waveform data. A detection of a cardiovascular condition, including PAH, is performed based upon the waveform data. In particular, PAH is detected if the waveform data is of a so-called prominent secondary peak (PSP) type. PSP waveforms include both a prominent primary pressure rise and a prominent secondary pressure rise between diastolic pulmonary pressure and systolic pulmonary pressure values.
Furthermore, the more general scope to detect and monitor pulmonary artery pressure (PAP) naturally includes the specific detection of PAH but in addition also enables early detection of Heart Failure by e.g. indirect monitoring of left ventricular end-diastolic pressure.